If amniotic fluid begins leaking during pregnancy, this can be cause for concern. Read on to learn more about the purpose of amniotic fluid, normal levels at various stages of pregnancy, and what leakage can indicate.
What Is Amniotic Fluid?
During pregnancy, the baby floats in amniotic fluid, which is contained inside of the amniotic sac. The amniotic fluid appears within the first 12 days after conception. Early in pregnancy, it is made mostly of water produced by the mother. However, later in pregnancy, the baby begins to swallow the fluid, and excrete it in the form of urine. By about 20 weeks of pregnancy, the amniotic fluid is made up entirely of fetal urine. It also contains important nutrients, antibodies, and hormones.
What Is the Purpose of Amniotic Fluid?
Amniotic fluid serves many functions. These include:
- Cushioning the fetus from physical pressures
- Cushioning the umbilical cord from physical pressures (i.e. stopping it from becoming compressed, which can restrict the flow of oxygenated blood and nutrients to the baby).
- Keeping the baby warm
- Preventing infection in the baby
- Helping the baby’s lungs and digestive system develop. The baby breathes and swallows the amniotic fluid, thereby practicing using muscles in the respiratory and digestive tracts.
- Helping the baby’s muscles and bones develop. The fluid allows the baby to float and move around inside the amniotic sac, which promotes proper development.
- Preventing fingers and toes from growing together. The amniotic fluid lubricates the baby’s extremities. If there is not enough amniotic fluid, there may be webbing (1).
What Is a Normal Amount of Amniotic Fluid?
The amount of amniotic fluid generally increases until approximately 36 weeks of pregnancy, when it reaches its highest point. Amniotic fluid levels throughout pregnancy may be as follows:
- Week 12 of pregnancy: 60 mL
- Week 16 of pregnancy: 175 mL
- Weeks 34-48 of pregnancy: 400-1,200 mL (2)
Toward the end of pregnancy, the amount of amniotic fluid should decrease in preparation for birth. Generally, the amniotic sac tears near the end of the first stage of labor. At this time, the remaining amniotic fluid begins to leak out through the cervix and vagina. This is often called a mother’s “water breaking” (1, 3). Some women will experience this as a sudden gush of fluid, but more often, it begins as a slow trickle (3). If this happens when a baby is at term and ready to be born, it is not a problem. However, if a woman’s water breaks or she begins leaking amniotic fluid early, this can lead to complications.
What Can Happen When Amniotic Fluid Leaks?
Although a very small amount of amniotic fluid leakage may be okay, too much can result in oligohydramnios (an abnormally low level of amniotic fluid), and a number of other complications. These include:
- Premature birth
- Slowed fetal growth
- Labor difficulties. For example, the umbilical cord may become compressed, and the baby may be deprived of oxygen.
- Increased likelihood of cesarean delivery, which may be necessary to prevent fetal oxygen deprivation and other complications.
- Infection. If there is a tear or puncture in the amniotic membranes, dangerous bacteria can enter the uterus and harm the baby. (2).
- Hypoxic ischemic encephalopthy (HIE) (4)
Leaking amniotic fluid can indicate premature rupture of membranes (PROM), a complication in which the amniotic sac ruptures (the mother’s water breaks) before the baby is in the correct position for birth. PROM occurs in approximately two percent of pregnancies, and can result in infection, umbilical cord prolapse, and other issues.
PROM can also occur prematurely, in which case it is known as preterm premature rupture of membranes (PPROM). PPROM comes with the added risk of causing premature birth (5).
Oligohydramnios, PROM, PPROM, and other complications associated with leaking amniotic fluid can be very dangerous. These issues can cause serious birth injuries, illnesses, and lifelong disabilities, including the following (among others):
How Do Doctors Measure Amniotic Fluid?
Throughout a woman’s pregnancy, her doctor should monitor the amount of amniotic fluid using ultrasound technology. There are two calculations that can be used: the amniotic fluid index (AFI) and the maximum vertical pocket (MPV) (2).
These tests can be used to diagnose oligohydramnios or polyhydramnios (abnormally high levels of amniotic fluid, the opposite of oligohydramnios). Both of these conditions serve as a warning sign that the mother and baby may be in danger.
Oligohydramnios occurs in about four percent of all pregnancies. It is more common in postterm pregnancies – that is, when a baby has not yet been delivered by 40 weeks. It can increase the risk of complications, especially umbilical cord prolapse. Sometimes, women with oligohydramnios will need cesarean deliveries. Doctors may also recommend an amnioinfusion (a procedure in which saline is infused into the uterus), increased hydration (either oral or through an IV), and bed rest (1).
Polyhydramnios occurs in about one percent of all pregnancies. Mild cases may resolve without treatment, but more severe cases can require amnioreduction, medications to reduce the amount of fetal urine (which can also put a fetus’s heart health at risk, so doctors must weigh the pros and cons very carefully, and closely monitor the baby), early induction, or bed rest (6).
How Can I Determine Whether Amniotic Fluid Is Leaking?
The signs and symptoms of amniotic fluid leakage can be subtle. Healthline explains this with a useful analogy:
“Think of your amniotic sac like a water balloon. While it’s possible to break the water balloon, causing a strong gush of fluid (known as your water breaking), it’s also possible that a small hole could develop in the sac. This can result in a slow leak of amniotic fluid.”
During pregnancy, women may also experience leakage of urine (caused by the uterus pressing on the bladder) and excess vaginal fluid (which will help ease the birthing process). Distinguishing between these substances can be challenging, but the following are some general patterns:
- Urine usually has a smell and is yellow in color. Although pregnant women often do have some urine leakage, they generally maintain some level of control over when it is released, while this is not the case for vaginal fluid or amniotic fluid. Therefore, if you concentrate on “holding it,” and are still leaking fluid, it is likely not urine.
- Vaginal fluid is usually white or yellow-ish. It is unlikely to soak through underwear.
- Amniotic fluid has no smell. It can be clear, have white specks, or contain small amounts of mucus or blood. It is more likely than vaginal fluid to saturate underwear.
In order to determine whether a substance is amniotic fluid, Healthline recommends first emptying the bladder, and then wearing a sanitary pad or liner for 30 minutes to an hour. This will make it easier to examine (2).
When Should I Call a Doctor?
If you are have expelled a substantial amount of fluid, call your doctor immediately, because this may indicate your membranes have ruptured (1, 2).
You should also call your doctor immediately if the leaked fluid has a green or brownish yellow color. This may mean that your baby has defecated inside of the womb (or passed meconium); if this enters the baby’s lungs, it can be very dangerous. This complication is called meconium aspiration syndrome, and it requires prompt medical attention (1).
If you are unsure whether you have leaked amniotic fluid, the best thing to do is call a doctor right away. Remember that the distinction between these substances is not always obvious, and that it is your doctor’s job to help you when you have a concern!
- Medical News Today – What’s to know about amniotic fluid?
- Healthline – Leaking Amniotic Fluid During Pregnancy: What Does It Feel Like?
- American Pregnancy Association – Signs of Labor
- Pediatrics – Antepartum and Intrapartum Factors Preceding Neonatal Hypoxic-Ischemic Encephalopathy
- Healthline – Tests for Premature Rupture of Membranes
- American Pregnancy Association – Polyhydramnios: High Amniotic Fluid During Pregnancy
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